Melatonin (N-acetyl-5-methoxytryptamine), which is a hormone synthesized and secreted principally in the pineal gland, increases in dark environments and decreases in light environments. Melatonin acts suppressively on pigment cells and the female gonads, and acts as a synchronous factor of biological clock while taking part in transmittance of photoperiodic code. Therefore, melatonin is expected to be usable for the treatment of diseases related to melatonin activity, such as reproductive and endocrinic disorders, sleep-awake rhythm disorders, jet-lag syndrome, various disorders related to aging and the like. It has been clarified that the production amount of melatonin decreases with aging and there is a report documenting that retention of the production amount of melatonin could prevent aging itself [Ann. N.Y. Acad. Sci., vol. 719, pages 456-460, (1994) (non-patent document 1)]. However, since melatonin is easily metabolized by metabolic enzymes in vivo [Clinical Examinations, vol. 38, No. 11, pages 282-284 (1994) (non-patent document 2)]. Therefore, melatonin is not entirely suitable as a drug.
WO 97/32871 (patent document 1) and U.S. Pat. No. 6,034,239 (patent document 2) disclose a compound represented by the formula:
wherein R1 represents an optionally substituted hydrocarbon group, an optionally substituted amino group or an optionally substituted heterocyclic group; R2 represents a hydrogen atom or an optionally substituted hydrocarbon group; R3 represents a hydrogen atom, an optionally substituted hydrocarbon group or an optionally substituted heterocyclic group; X represents CHR4, NR4, O or S wherein R4 represents a hydrogen atom or an optionally substituted hydrocarbon group; Y represents C, CH or N, provided that when X is CH2, Y is C or CH; is a single bond or a double bond,ring A represents an optionally substituted 5- to 7-membered oxygen-containing heterocyclic ring; ring B represents an optionally substituted benzene ring; and m represents an integer of 1 to 4, or a salt thereof and the like, which has an affinity for melatonin receptor and is useful as a therapeutic agent for sleep disorder and the like.
U.S. Pat. No. 5,633,276 (patent document 3) discloses a compound represented by the formula
wherein R1 represents hydrogen, halogen or C1-6 alkyl; R2 represents a group represented by —CR3R4(CH2)pNR5COR6; R3, R4 and R5 are the same or different and each represents hydrogen or C1-6 alkyl; R6 represents C1-6 alkyl or C3-7 cycloalkyl; n represents 2, 3 or 4; and p represents 1, 2, 3 or 4, which is useful as a therapeutic agent for conditions associated with a disturbed functioning of the melatonin system and the like.
WO 2006/27474 (patent document 4) discloses a compound represented by the formula
wherein A represents —NHCOR1 or —CONHR1; R1 represents C1-6 alkyl, C3-6 cycloalkyl etc.; R2 represents alkoxy; and R3 represents aryl, arylalkyl or aroyl, which is useful as a therapeutic agent for conditions associated with a disturbed functioning of the melatonin system and the like.
Bioorganic & Medicinal Chemistry, vol. 14, pages 1949-1958 (2006) (non-patent document 3) discloses the following melatonin receptor agonist:
wherein R2 represents H or Ph, and R3 represents Me, Et or Pr.
U.S. Pat. No. 5,843,986 (patent document 5) and U.S. Pat. No. 5,998,461 (patent document 6) describe a tricyclic amide compound as a therapeutic agent for a disorder of the melatoninergic system.    patent document 1: WO 97/32871    patent document 2: U.S. Pat. No. 6,034,239    patent document 3: U.S. Pat. No. 5,633,276    patent document 4: WO 2006/27474    patent document 5: U.S. Pat. No. 5,843,986    patent document 6: U.S. Pat. No. 5,998,461    non-patent document 1: Ann. N.Y. Acad. Sci., vol. 719, pages 456-460 (1994)    non-patent document 2: Clinical Examinations, vol. 38, No. 11, pages 282-284 (1994)    non-patent document 3: Bioorganic & Medicinal Chemistry, vol. 14, pages 1949-1958 (2006)